Construction work to transform the London 2012 Olympic Stadium into a permanent sports and cultural venue has begun at the Queen Elizabeth Olympic Park.

During the work the stadium's capacity will be reduced from 80,000 to around 60,000 and a new roof will be fitted, covering every seat in the ground and improving the venue's acoustics.

New retractable seating will also be installed so the lower bowl can be protracted and retracted depending on the type of event taking place, allowing closer pitch side football views while retaining an international class running track.

Work is expected to be completed in time for the stadium to host five games during the Rugby World Cup in 2015. West Ham United Football Club is due to move into the stadium and make it its permanent home in 2016.

London Legacy Development Corporation (LLDC) has agreed contracts worth more than £67m for the redevelopment on behalf of E20 Stadium Company - a joint partnership between LLDC and London Newham Council set up to manage the venue. Carey's has been appointed lead contractor for the project.

LLDC chief executive Dennis Hone said: "These works will ensure the Stadium will be a flexible venue used throughout the year, delivering a truly lasting legacy in east London.

"From the lighting of the cauldron to 2012 stars like Mo Farah, Hannah Cockcroft and Usain Bolt storming to victory, this iconic Stadium holds some special memories. Today paves the way for the Stadium's next chapter and I am sure it will host many more inspirational moments over the decades to come."

The stadium was designed by architects Populous and was built at an estimated cost of £486m.